Microtubule-associated protein τ from bovine brain reacted on immunoblots and on enzyme-linked immunosorbent assay with a monoclonal antibody, Alz 50, which has previously been found to bind to an Alzheimer disease-specific antigen. The apparent affinity of binding of Alz 50 to τ was 2.1 x 10-9 M on competitive enzyme-linked immunosorbent assay, and it was in the same range as for Tau-1 (0.5 x 10-9 M), an antibody raised against purified bovine τ proteins. Immunoblotting of trypsin-digested τ revealed differences between Alz 50 and Tau-1 binding sites. The binding of both antibodies to τ was not affected by prior treatment with phosphatase, indicating that the cross-reactivity of Alz 50 with τ is due to the presence of phosphate-independent epitope. This epitope then differs from phosphate-dependent τ epitopes often shared with other cytoskeletal proteins. Alz 50 and Tau-1 binding sites were present in all isoelectric (pI 6-8) and molecular weight variants of τ. In contrast, phosphate-dependent epitopes recognized by another τ-reactive antibody (NP 14) were found mostly in acidic τ variants. Similarly to τ proteins from bovine brain, τ-enriched preparations from normal human brain contained Alz 50 and Tau-1 reactive sites in all isoelectric (pI 6.5-8.5) and molecular weight variants. Our observation of Alz 50 cross-reactivity with τ suggests a relationship between τ and the novel protein identified recently in Alzheimer brains.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of Biological Chemistry|
|State||Published - 1988|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology